Fig. 1

Aze fits in the active site of both Hs AlaRS and ProRS. a Structures of proline (Pro), azetidine-2-carboxylic acid (Aze), and alanine (Ala). Structure of Hs AlaRS with b Ala-SA or c Aze-SA in the active site. d Tt ProRS structure with Pro-SA in the active site. e Hs ProRS structure with Aze-SA in the active site